Semiconductor reliability testing requires accurate electrical stress and measurements under tight temperature control. Typical test temperatures range from slightly above room temperature to Tmax˜350° C., while spatial temperature variations are often exacerbated by differences in self (Joule) heating from one Device Under Test (DUT) to another. Furthermore, DUT sockets, printed circuit boards (DUT boards), and insulation materials, easily available for temperatures below 250° C., are hard to make for higher temperatures.
Convection ovens, optimized for the required temperature range, have been used by the industry for many years. However, these ovens have two inherent shortcomings, which limit their performance: (i) the large volume associated with their heating mechanism (hot air convection) makes them impractical when a small number (5-15) of DUTs per temperature is needed; (ii) by definition, temperature control is global, so local temperature variations and non-uniformities are often problematic.
A different approach has led to a small oven unit, integrated with a single DUT board (prior art: U.S. Pat. No. 6,097,200), where the tested DUTs are maintained at a controlled temperature within the required range. The concept is based on an electrically heated surface, which transfers the heat via several metal plates to a radiator, positioned very closely to the DUTs. While the unit is compact and does not involve air convection, heating is global for the entire unit, with a single temperature sensor on the DUT board. Another limitation is the need to change the DUT board whenever the pin assignment of the packaged DUTs is changed.